1. Field of the Invention
The present invention relates to liquid crystal display device and, more particularly, to a method of manufacturing an in-plane switching mode liquid crystal display device.
2. Description of the Related Art
An in-plane switching mode liquid crystal display device, which is widely used as a flat panel display device having a wide viewing angle, uses a color filter consisting of red R, green G and blue B filters for a color display.
In order to manufacture such an in-plane switching mode liquid crystal display device, methods such as dye, pigment dispersion, electrodeposition, and print have been generally utilized, which will be described below.
First, the dye method refers to a method of dying a dyable and photosensitive resin on a transparent substrate with a dying solution after exposing and developing. The pigment dispersion method is typically divided into a method of exposing and developing a photosensitive color resin dispersed with a pigment on a photosensitive resin after coating, and a method of etching a non-photosensitive material dispersed with a pigment in a polyimide by using a photoresist. The electrodeposition method refers to a method of depositing a polymer resin on an electrode by dissolving and dispersing in a solvent. The print method refers to a method of transferring an ink dispersed with a pigment to a resin.
In the above described related art methods of manufacturing a color filter, the step of forming an overcoat layer is employed for preventing leakage of light by minimizing a stepped difference (or surface unevenness) of an overlapped part between a light-shielding black matrix and a color filter layer.
The in-plane switching mode liquid crystal display and a method of manufacturing a color filter in the related art will be described in more detail with reference to the accompanying drawings.
FIG. 1 is a view showing a related art in-plane switching mode liquid crystal display device. In FIG. 1, the in-plane switching mode liquid crystal display device includes a gate line 1 and a data line 2 arranged longitudinally and transversely on a transparent first substrate 10 (refer to FIG. 2). Even though the gate line 1 and the data line 2 define a pixel area and a liquid crystal display panel is composed of a plurality of pixel areas, only a single pixel area is shown in FIG. 1 for the sake of convenience of explanation. In the pixel area, the gate line 1 and a parallel common line 16 are arranged and a thin film transistor is formed on a crossing point of the gate line 1 and the data line 2.
FIG. 2 is a cross-sectional view taken along line A-A′ of FIG. 1. In FIG. 2, the thin film transistor TFT includes a gate electrode 3, a gate insulation film 19, a source electrode 4a, a drain electrode 4b, a semiconductor layer 12, and an ohmic contact layer 13. The gate electrode 3 and the source electrode 4a are respectively connected to the gate line 1 and the data line 2 (refer to FIG. 1), and the gate insulation film 19 is deposited over the whole substrate.
The pixel area is formed with a common electrode 7 and a data electrode 8 which are arranged in parallel to each other for applying horizontal or in-plane electric fields. The common electrode 7 is formed on the first substrate 10 simultaneously with the gate electrode 3 and connected to the common line 16, and the data electrode 8 is formed on the gate insulation film 19 simultaneously with the source electrode 4a and the drain electrode 4b and connected to the drain electrode 4b of the TFT. Further, a protective layer 22 and a first alignment film 20a are formed on the whole first substrate 10.
A second substrate 11 is formed with a black matrix 15 and a color filter layer 25 for preventing leakage of light in the vicinity of the TFT, the gate line 1 and the data line 2 (refer to FIG. 1). A second alignment film 20b is formed thereon. Further, a liquid crystal layer 30 is formed between the first substrate 10 and the second substrate 11.
In the in-plane switching liquid crystal display device of the above described structure, liquid crystal elements in the liquid crystal layer 30 are aligned according to the alignment directions of the first alignment film 20a and the second alignment film 20b when no voltage is applied. On the other hand, if a voltage is applied between the common electrode 7 and the data electrode 8, an electric field that is parallel to the surface of the first substrate 10 is applied between the common electrode 7 and the data electrode 8, such that the liquid crystal elements in the liquid crystal layer 30 are switched by the transverse electric field. Accordingly, the liquid crystal elements in the liquid crystal layer 30 are aligned almost vertically to an extension direction of the common electrode 7 and the data electrode 8. As described above, since the liquid crystal elements in the liquid crystal layer 30 always switch on the same surface, grey level conversion does not occur when viewing from angles in the vertical and horizontal directions.
FIG. 3A to FIG. 3G are views for showing a related art process of coating an overcoat layer for removing a stepped difference between a black matrix for light-shielding and a color filter layer. First, as shown in FIG. 3A, the black matrix 15 is formed on the first substrate 11, a dyable photosensitive film 100 is coated thereon as shown in FIG. 3B and front exposed to UV light using a mask 101 as shown in FIG. 3C. A color filter layer 25 is thus formed as shown in FIG. 3D. Desired colors R, G and B are dyed and fixed as shown in FIG. 3E. By repeating the steps of FIG. 3B to FIG. 3E continuously, color filter layers of R, G and B 25 are formed on the glass substrate 11. However, it is very difficult to maintain a uniform thickness since such color filter layers R, G, and B 25 are formed separately. Accordingly, an overcoat layer 102 is coated thereon to planarize the color filter layer 25 and remove the stepped difference or unevenness of the overlapped part of the black matrix for light-shielding 15 and the color filter layer 25.
FIG. 4A to FIG. 4C are detailed views showing a related art process of coating an overcoat layer. The glass substrate, including the black matrix 15 and the color filter layer 25, is coated with the overcoat layer 102 with a polymer as shown in FIG. 4A. A mask 101 forms a pattern on the substrate which is coated with the overcoat layer 102 and exposed to ultraviolet light as shown in FIG. 4B. The overcoat layer 102 is removed by dispersing a developing solution on the substrate of which UV exposure is complete for forming a pattern. The overcoat layer 102 on the pattern is cured by post baking as shown in FIG. 4C. The overcoat layer 102 also functions to protect the color filter layer 25.
To planarize the color filter layer using the related art coating process of the overcoat layer, various processes are required including an exposing process, as described above. That is, to prevent the overcoat layer from being damaged during a rubbing process, an exposing process using an exposing type material and a developing process are used. However, such exposing and developing process is complicated and increases manufacturing cost, thereby decreasing productivity.